Three types of USCT images are conventionally produced: reflectivity, SOS, and acoustic attenuation (AA) [1]}.
Reflectivity images can be reconstructed by use of integral geometry-based approaches that are similar to the delay-and-sum methods widely employed in conventional B-mode imaging.
The majority of the SOS and AA reconstruction methods investigated to date are generally based on two categories: approximated wave equation methods [2]}, [3]}, [4]}, and full-waveform inversion (FWI) methods [5]}, [6]}, [7]}, [8]}.
Because FWI methods take high-order refraction and diffraction effects into account, they can produce images that possess higher spatial resolution images than those produced by use of linearized or approximate methods[9]}, [8]}, [5]}.
However, FWI is computationally expensive and memory burdensome, especially for 3D problems, thus hampering the widespread application of FWI to USCT breast imaging. Moreover, FWI suffers of the so-called cycle skipping phenomenon[12]}, thus requiring an accurate initial estimate of the SOS map to ensure convergence to a useful solution.
As a result, there is still an imperative need to systematically investigate and optimize USCT reconstruction methods by means of computer-simulation studies.
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